Trailer brake control system

ABSTRACT

A trailer brake control system for a tractor-trailer arrangement which comprises a deceleration transmitter located at the tractor for generating electrical signals as a function of the braking or deceleration action exerted at the tractor. An electronic circuit serves to amplify the generated electrical signals. Mechanisms responsive to the amplified electrical signals serve to operate braking apparatus arranged at the trailer.

United States Patent Tschannen Dec, 18, 1973 [5 TRAILER BRAKE CONTROLSYSTEM 3,574,414 4/1971 Jacob 303/7 2,032,177 2/1936 Logan, .Ir. 303/24A Inventor: l Tschannen Gorgler 2,193,910 3 1940 Wilson 303/21 ccswltlerland 3,275,835 9/1966 Morrison 250/215 x [73] Assignee: BekaSt-Aubin S.A., St-Aubin, 1

Neuchatel, Switzerland FOREIGN PATENTS OR APPLICATIONS [22] Filed: May17, 1971 2,024,406 12/1970 Germany 188/112 Appl. No.: 143,818

Primary Examiner-Trygve M. Blix Assistant ExaminerStephen G. KuninAttorney-Werner W. Kleeman [57] ABSTRACT A trailer brake control systemfor a tractor-trailer arrangement which comprises a decelerationtransmitter located at the tractor for generating electrical signals asa function of the braking or deceleration action exerted at the tractor.An electronic circuit serves to amplify the generated electricalsignals. Mechanisms responsive to the amplified electrical signals serveto operate braking apparatus arranged at the trailer.

1 Claim, 6 Drawing Figures 2 1. .222 l T 1 89 I i 82 102 91. a3 50 a4 99as l a5 i 100 51 I l 1 s1 93 I 51 l 91 95101 l 101. l l 92 1 WWW 197a3.779.612

SHEET 10F 4 DECELERAT. TRANS BRAKE TRANSIMITT. AMPL'F'ER DUC\ER UNITPOWER SOURC.E

HAND BRAKE l 3 SWITCH FIG. 1

BRAKE CYCLINDER 0 35 2 35d 15 1a NVENTO FIG. 3

HHMS TScI-IRNNEN BLT-r9512 PATENTEU an: 18 ms SHEET 2 UF 4 /N vENTo I?HBNS Tswnnuw N wewuw. klm

TRAILER BRAKE CONTROL SYSTEM BACKGROUND OF THE INVENTION The presentinvention broadly relates to brake control systems for motor vehiclesand, more particularly, deals with a new and improved trailer brakecontrol system. The prior art has already proposed different trailerbrake control devices or systems which are controlled pneumatically bythe tractor vehicle. Yet, the state-ofthe-art trailer brake controlsystem proposed previously possess the disadvantage that they require arather long response time. In brake systems which have been constructedfor the tractorand trailer vehicles, it is readily possible tohydraulically control the trailer brake control system from that of thetraction vehicle. However, in the event that a trailer brake controlsystem is to be subsequently mounted at the hydraulic brake circuit ofthe traction vehicle then, as a practical matter, difficulties arise,primarily because the manufacture of the vehicles will not honor anyguarantee as soon as modifications are undertaken at the original brakesystem. Therefore, repair service stations also refuse to undertake suchmodifications at the brake system of such vehicles. Similar problemswould arise if a mechanical-electrical transmitter is connected, throughsimilar modifications at the hydraulic brake system of the tractorvehicle, and from which transmitter then the trailer brake controlsystem would be controlled.

SUMMARY OF THE INVENTION Accordingly, it will be recognised that thereis still present a real need in the art for a trailer brake controldevice or system which is not associated with the aforementioneddisadvantages of the prior art and which satisfactorily fulfills theneed still existent in the prior art. Hence a primary object of thisinvention is to provide just such trailer brake control system whichsatisfactorily and reliably fulfills the need in the art and overcomesthe aforementioned drawbacks prevailing in the state-of-the-art devicesof this type.

Still another and more specific object of the present invention relatesto the provision of a novel trailer brake control system which affordsacceptable economics concerning manufacturing and installation costs,which possesses a short response-time and therefore is primarilyelectrically controlled, and additionally, wherein the novel brakecontrol system of the invention does not require any modification oralteration at the hydraulic brake system of the tractor vehicle.

The invention is based upon the concepts of electrically measuring thedecelerations arising upon braking apparent as the description proceeds,it should be understood that one embodiment of trailer brake controlsystem designed according to the teachings of the present invention ismanifested by the feature that there are provided:

a. a mercury-circular pendulum-deceleration transmitter installed at thetractor, this transmitter delivering electrical signals during brakingor deceleration of the tractor, wherein the intensity of such electricalsignals are approximately inversely proportional to the momentarybraking or deceleration of the tractor;

b. electronic means for amplifying these signals;

c. an electromagnet serving as electro-mechanical transducer means, andthe armature of which electromagnet moves approximately proportional tothe amplified signals in opposition to a return or restoring force; and

d. vacuum brake valve means or compressed air brake valve means actuatedby the armature of the electromagnet, such brake valve means actuating avacuum brake cylinderor compressed air brake cylinder respectively.

A preferred physical manifestation of such inventive system or apparatusis further manifested by the features that the electronic means embodiesa power transistor, the collector of which is coupled with the windingof the electromagnet, a switching transistor which can be controlled asa function of the brake light switch of the tractor, and a controltransistor influenced by the mercury-circular pendulum-braking ordeceleration transmitter, and wherein the switching transistor and thecontrol transistor are connected with the base of the power transistor.

Now in accordance with an improved embodiment of the inventive trailerbrake control system such is manifested by the features that there areprovided:

a. a circular pendulum-deceleration or braking transmitter which isinstalled at the tractor and which, during braking of the tractor,controls the quantity of light received by a photoelement from a lightsource supplied by a constant voltage, so that at the photoelement theresistance thereof increases or decreases in proportion to the momentarydeceleration or braking of the tractor;

b. electronic means for delivering as a function of the momentaryresistance value of the photoelement an electrical signal which is in apredetermined relationship to the momentary deceleration or brakingaction; and

c. an electro-pneumatic transducer means which, as a function of theelectrical signal, acts upon a vacuum cylinder or a compressed air brakecylinder, or an electrically actuated brake, which are actuated as afunction of the electrical signal.

The photoelement preferably consists of a photoconductive cell, such asa photoresistor. The electronic means preferably comprises anoperational amplifier and at least one power transistor. Theelectropneumatic device preferably comprises an electrodynamictransducer which, in cooperation with a reaction unit, is finelymechanically coupled with a pneumatic control element responding withlow reactive effect and which in turn acts, via a relay valve, upon thepiston of a brake cylinder-piston unit.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood and objects other than those set forth above, will becomeapparent when consideration is given to the following detaileddescription thereof. Such description makes reference to the annexeddrawings wherein:

FIG. 1 is a block circuit diagram of a first embodiment of the inventivetrailer brake control apparatus or system;

FIG. 2 is a circuit diagram showing details of the system of FIG. 1, andspecifically illustrating same equipped with vacuum brake control meansat the trailer;

FIG. 3 is a modification of the portion of the system shown at the rightof the circuit of FIG. 2, wherein such is equipped with compressed airbrake control means;

FIG. 4 is a block circuit diagram of a second embodiment of theinventive system;

FIG. 5 is a circuit diagram illustrating details of the system depictedin FIG. 4, and specifically equipped with vacuum brake control means atthe trailer; and

FIG. 6 is a similar circuit diagram to that shown in FIG. 5 of a thirdembodiment of the invention wherein the trailer is equipped withelectrically actuated brakes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now thedrawings, and considering initially the embodiment depicted in FIGS. 1to 3 inclusive, it will be understood that with the block diagram ofFIG. 1 there has been represented the principles of the construction ofthis first embodiment of the inventive trailer brake control system. Tothis end, there will be understood that there is provided a braking ordeceleration transmitter, which is here shown as a mercurycircularpendulum-deceleration transmitter 1 which is installed at the tractor ordrawing vehicle. This braking or deceleration transmitter 1 responds toeach braking or deceleration of the tractor, delivering electricalsignals to an electronic amplifier 2, the intensity of which isapproximately inversely proportional to the momentary deceleration orbraking of the tractor. A power source, such as a battery 3 serves tosupply power to the amplifier 2. Reference character 4 denotes a brakelight switch means which is responsive in the normal manner to actuationof the hydraulic brake device 5 of the tractor through the agency of thefoot or board plate 6. There is also provided a switch means 7 which isresponsive to actuation of the hand brake device 8 of the tractor.Reference character 9 indicates a trans ducer which here consists ofelectromagnetic means and is supplied by the amplifier 2 with theamplified electrical signals, transducer 9 having an armature which ismoved approximately proportional to the intensity of the amplifiedsignals against the restoring force of a spring, as will be more fullyexplained hereinafter. Also illustrated in FIG. 1 there is providedvacuum brake valve means or compressed air brake valve means, indicatedat reference character 10, which are controlled by the transducer 9 andwhich act upon vacuumor compressed air brake cylinder means of thetrailer, again as will be more fully explained hereinafter. Amplifier 2only functions when the brake light switch means 4 is closed, on theother hand does not function when the switch means 7 is closed owing toactuation of the hand brake device 8.

Turning now to the circuit diagram of FIG. 2 which provides details ofthe arrangement illustrated in block form in FIG. 1 it will be seen thatonce again reference character 3 designates the power supply battery,reference character 5 the hydraulic brake system of the tractor togetherwith the associated foot board or plate 6, the brake light switch means4 and the brake lights 1 1, reference character 8 indicating the handbrake device with the associated switch means 7. The block 12 shown inphantom lines at the left of FIG. 2 contains the components of thesystem which are installed at the tractor, while the block 13 shownsimilarly in phantom lines but at the left of FIG. 2 contains thecomponents of the system installed at the trailer. Reference character14 denotes an electrical conductor coupling arrangement for coupling therelevant electrical components of the system located at the tractor withthe transducer. Reference character 15 indicates a hose conduit couplingarrangement which connects a negative pressure line 16 coupled with thesuction pipe of the tractor engine with a line or conduit 17 connectedwith a negative pressure container 18. Here also the mercurycircularpendulum-deceleration transmitter is designated by referencecharacter 1. This deceleration transmitter 1 functions in such a mannerthat the mercury, during zero deceleration or braking, connects contact1a with contact lb, but as the braking or deceleration increases contactIn is successively connected with the further contacts 10, 1d, 1e, If,and 1g. Reference characters 38, 19, 20, 21, 22, 23, 24, 25, 26 and 27represent different electrical resistors, wherein the last fiveresistors 23, 24, 25, 26 and 27 are associated with the braking ordeceleration transmitter 1.

The electrical arrangement will also be understood to contain aswitching transistor 28, here in the form of a npn-transistor, which iscontrolled as a function of the brake light switch means 4, apnp-control transistor 29 influenced by the deceleration transmitter l,and a pup-power transistor 30, the collector of which is operativelycoupled with the winding 9a of the electromagnetic transducer means 9.Now when the electro-magnetic-transducer means 9 is energized thearmature 9b thereof is attracted against the restoring force of a spring31. The armature 9b then acts upon the movable elements 32, 33 of aconventional precontrol valve unit 34 which functions in force-reactivemanner and the output of which is connected with the input of aconventional relay valve 35 which, in turn, has its output operativelycoupled with the vacuum brake cylinder or cylinders 36 of the vehicle.

The mode of operation of the electrical hardware of the described systemis as follows:

Now if neither the foot brake 6 or the hand brake 8 of the tractor isactuated, then the emitter of the power transistor 30 is connected viaswitch means 7 with ground, that is to say with the positive terminal ofthe supply battery 3 and its collector is connected via the winding orcoil 9a and the ignition switch 37 with the negative pole or terminal ofbattery 3. A maximum current flow exists through the winding 9a. Acontrol current is delivered to the base of the power transistor 30through the agency of the switching transistor 28 which is conductive,switching transistor 28 having its collector connected via the resistor38 with the base of power transistor 30, as shown. Switching transistor28 is conductive because its base is supplied via the voltage divider19, 20 with a potential which is positive with respect to the collectorof the switching transistor 28. The one resistor 19 of this voltagedivider 19, 20 is coupled with the negative terminal of the supplybattery 3 and the other resistor 20 has suppled thereto a positivepotential through the agency of a terminal of the brake light switchmeans 4 and the brake light lamps 11. The base of the control transistor29 has delivered thereto a potential which is positive in relation toits emitter, this causing the control transistor 29 to be nonconductiveindependent of the operating condition of the braking or decelerationtransmitter 1.

Now if upon actuation of the foot brake of the traction vehicle ortractor the brake light switch means 4 is closed, then, on the one handthe resistor of the voltage divider 19, 20 is connected with the minusterminal of the supply battery 3, with the result that the base of theswitching transistor 28 is no longer positively pre-biased and thisswitching transistor therefore is blocked and, on the other hand, thebase of the control transistor 29 has delivered thereto a negativepotential or voltage via the resistors 22 to 27 and the deceleration orbraking transmitter ll, whereby depending upon the braking ordeceleration of the tractor which has been discerned at the decelerationtransmitter 1 a larger or smaller number of the resistors 22 to 27 willbe connected in series. For instance, if the brake peddle is onlyslightly tapped, so that although the brake lights 11 light up, still noreal braking or deceleration occurs, then only the resistor 22 isconnected in series with the base of the control transistor 29 and thecurrent flowing through this control transistor 29, and which isdelivered to the base of the power transistor 30, is practically of thesame magnitude as that current which previously flowed through theconductive switching transistor 28. The excitation current at theelectromagnet winding 9a has momentarily remained the same. However, asa function of the increasing braking or deceleration one or more of thefurther resistors 23 to 27 will be connected in series with the base ofthe control transistor 29, so that the control current for the powertransistor 30 becomes smaller as the braking or deceleration increases.The excitation current flowing through the electromagnet winding 9a alsobecomes proportionally smaller as a function of the decrease of thecontrol current.

For reasons of security the above-described electrical portion of thesystem functions according to the socalled rest current principle. Inthe event that the power supply or a circuit component becomesinoperable then automatically braking of the trailer is initiated.

The mode of operation of the mechanical-pneumatic portion of the systemillustrated at the right of FIG. 2 and serving to supply the brakecylinder with negative pressure need only be briefly considered and isas follows:

If no braking action is initiated then the force of the spring 31 is ofthe same magnitude as the then small force of the electromagnet 9.Atmospheric pressure prevails in the chambers or spaces 34a, 34b of theprecontrol valve 34 and in the chambers or spaces a, 35b of the relayvalve 35.

As the braking or deceleration action increases, as explained above, theforce exerted by the electromagnet 9 becomes smaller. Therefore, thepre-control valve spindle 32 is increasingly raised by the action of thespring 31, and the opening at the supply seat 340 is increasinglyenlarged or opened and that at the venting or aeration seat 34d isclosed. Thus, within the chamber or compartment 35a of the relay valve35 there prevails a more or less large negative pressure or vacuum, thediaphragm piston 350 is raised, the opening at the supply seat 35d isopen and that at the venting seat 35a is closed. The more or less largenegative pressure or vacuum is supplied to the brake cylinder 36.

The mode of operation of the mechanical-pneumatic portion of the systemillustrated in FIG. 3 and designed for delivering compressed air to thebrake cylinder is as follows:

In the non-braked condition of the system atmospheric pressure at thepre-control valve 34' moves through the opening at the venting seat 34d(the supply seat 340' is closed) and arrives at the compartment 35a ofthe relay valve 35'. The valve element 35b of the relay valve 35 is thenraised and only atmospheric pressure moves through the opening at theventing seat 35c (that at the supply seat 35d is closed) and enters thebrake cylinder 36'.

When there has been attained a more or less braked condition thencompressed air moves out of the container 18' through the opening of thesupply seat 340' of the pre-control valve 34' (that at the venting seat34d is closed) and arrives at the compartment 35a of the relay valve 35.Hence at the relay valve 35' the reaction piston 35b' is downwardlydisplaced, while closing the opening at the venting seat 35c and openingthat opening at the supply seat 35d. Consequently, the brake cylinder36' is more or less markedly impinged with compressed air.

Attention is now directed to the embodiment depicted in FIGS. 4 and 5.As is usual, in that embodiment tail or brake lights 51 are connectedvia a brake light switch 52 to a power source, here shown as the battery53. At a circular pendulum-deceleration indicator or transmitter 54which is to be installed at the tractor and supplied with a stabilizedvoltage there is produced an electrical signal which is proportional tothe deceleration which occurs during braking of the tractor vehicle.This signal is delivered through the agency of an input voltage dividerto an amplifier 55, as will be explained more fully hereinafter. Thesignal which has been amplified at the amplifier 55 controls anelectropneumatic transducer arrangement 56 which produces a forceproportional to this signal. With maximum signal intensity, which occursat an indirect braking system during the non-braked condition, thisforce is in equilibrium with a spring force and there does not appearany resultant force at a control valve forming the last element of theelectro-pneumatic transducer arrangement 56. As the signal intensitydecreases the force delivered at the electro-pneumatic transducerarrangement 56 also decreases. Between the constant spring force and thedecreasing force there exists a resultant differential force which canbe used for actuating the control valve, such control valve beingpractically reactive free in the sense that the input pressure and theoutput pressure practically have no influence upon the actuation force.At the electro-pneumatic transducer arrangement 56 the output pressureof the control valve is delivered to a differential diaphragm pistonsystem. At this differential diaphragm piston system the output pressureproduces a force which is equal to that of a preceeding connectedelectrodynamic transducer, and additionally such force is directedopposite to the force of the spring.

Owing to the feedback of the output pressure of the control valve thereis ensured that such, during a reduction in force of tYe electro-dynamictransducer, will be controlled for such length of time until the controlpressure at the differential piston system produces a force whichcorresponds to the reduction in force of the electro-dynamic transducer.A reduction or increase of the signal intensity at the input of theelectrodynamic transducer thus produces an exact corresponding reductionor increase, respectively, of the pressure in the control valve,provided that the trailer is equipped with a vacuum brake device. Whenusing a compressed air brake device or system a decrease in force at thetransducer results in analogous fashion in an increasing pressure at thecontrol valve. In order to obtain a characteristic of the control valvewhich is as free as possible of feedback and hysteresis it is necessaryto select the throughflow cross-section at the control valve to be verysmall; the throughflow quantities are insufficient for directlycontrolling the brake cylinder 57 of the trailer. Therefore, there mustbe connected between the control valve of the electropneumatictransducer arrangement 56 and such brake cylinder 57 a relay valve 58 ofknown construction.

Now while referring in particular to the circuit diagram of FIG. thedetails of the construction of this embodiment of inventive trailerbrake control system will now be considered. Initially, it is to beassumed that the apparatus construction depicted in FIG. 5 is located inits rest condition, in other words the brake light switch 52 is open,characteristic of the non-braked condition. The deceleration indicatoror transmitter 54 will be seen to embody a circular pendulum 59 which,during deceleration or braking of the tractor, oscillates about anelectrical light source 60, thereby screening to a greater or lesserextent the quantity of light which thus is directed from this lightsource 60 and falls upon a photoconductive element here shown as thephotoresistor 61. In order to stabilize the supply voltage for the lightsource 60 there are provided Zener diode 62 and a resistor 63.

Now the amplifier 55 discussed above will be seen to embody as itsprimary components an integrated operational amplifier 64 and at asubsequently connected power stage a transistor 65. An input voltagedivider 68, 70 is associated with the operational amplifier 64 and atwhich, as can be seen by referring to the circuitry of FIG. 5, aresistor 68 is arranged between the junction 66 and the supply conductor67, and between the junction 66 and a conductor 69 connected to groundthe photoresistor 61 and a standard resistor 70 in parallel connection.Furthermore, there is provided a feedback voltage divider in which thereis arranged to each side of the junction 71 the resistors 72 and 73respectively. At the circuit of the amplifier 55 which is of knownconstruction there are additionally provided the auxiliaryand protectiveresistors 74 to 78 and a capacitor 79. The output terminals of thisamplifier 55 are indicated at 80.

Now when the brake peddle is not actuated then the brake light switch 52is open. In this rest condition the one terminal of the light source 60is electrically coupled through the agency of the resistor 63, the brakelight 51 and ground with the positive terminal or pole of the battery 53and the other terminal of the light source 60 is directly connected viaground likewise with the positive terminal or pole of the battery 53.Hence the light source 60 does not illuminate. Consequently, noradiation of light appears at the photoresistor 61 and such possesses alarge resistance. At the junction 66 of the input voltage divider, theresistor 68 of which is connected via the supply conductor 67 with thepositive pole of the battery 53, there appears a voltage which ispositive with respect to ground, because the junction point between theresistors and 74 and the photoresistor 61 with which these resistors 70,74 are connected in parallel, is connected with ground.

The voltage which appears at the junction 66 is delivered through theagency of the protective resistor 75 to the non-inverting input 3 of theoperational amplifier 64. At the output 7 of this operational amplifier64 there are connected a load resistor 77 and the base of the transistor65 of the power stage. The collector of this transistor 65 is connectedwith ground and the emitter is connected through the agency of theimmersion or dip coil 83 of the hereinafter to be described transducerarrangement 56 with the supply conductor 67. The feedback voltagedivider encompassing the resistors 72 and 73 is connected in parallelwith respect to the immersion coil 83 and the feedback voltage which istapped-off at the junction 71 of such voltage divider is delivered tothe inverted input 4 of the operational amplifier 64 through the agencyof the protective resistor 76.

The resistors which form the input voltage divider and the feedbackvoltage divider are designed such that during the above-described restcondition the voltage delivered to the non-inverting input 3 of theoperational amplifier 64 is just large enough in magnitude that avoltage drop appears across the load resistor 77 which is sufficient topractically completely render the transistor 65 conductive. Therefore,the current flowing through the immersion coil 83 assumes is maximumvalue during the rest condition. The feedback ensures that the entireamplifier 55 will possess a constant gain or amplification factor, eventhen if the voltage delivered by the battery 53 fluctuates. Thecapacitor 79 reduces amplification at high frequencies, resulting in asuppression of the tendency to oscillate brought about by the feedback.

The electro-pneumatic transducer device 56 possesses as its primarycomponents an electro-dynamic transducer 81 equipped with a permanentmagnet 82 and the immersion coil 83, furthermore a control valve 84 witha housing 85 and a plate-shaped movable valve element 86, and finally areaction unit 87. The reaction unit 87 is equipped with a differentialdiaphragm piston 88 operating within a housing 89 and possessing a rodmember 90 which at its free end is connected with one end of a tensionspring 91. The other end of this tension spring 91 is suspended at anadjustment screw 92 serving to regulate the pre-bias of this spring 91.

A rod member 93 carrying the effective element, namely the movable valveelement 86 of the control valve 84 is mounted to be tiltable in closeproximity to this effective element 86 at the housing 85. Furthermore,this rod member 93 extends practically without play through the pistonrod 90 and carries at its free end the immersion coil 83 of theelectro-dynamic transducer 81.

In the rest condition, in other words when the brake light switch isopen maximum current is delivered to the immersion coil 83 from theamplifier 55 via the connection conductors 94, resulting in thisimmersion or dip coil 83 completely immersing into the permanent magnet82. Consequently, the rod 93 is tilted in clockwise direction about thepivot position at the housing 85 against the resistance of the spring91. In so doing, the effective valve component 86 during thiscorresponding tilting or pivoting movement maintains the mouth 95 of asuction line 96 closed. Communicating with this suction line 96 is avacuum container or vessel 97, vacuum container 97 being connected witha negative pressure source 98, for instance arranged at the drive motoror engine of the tractor. At the same time as the mouth 95 of thesuction line 96 is closed by the effective valve component 86 thiseffective control valve component 86 simultaneously frees the mouth 99of a' channel 100 communicating with atmosphere. Hence, within thecompartment 101 of the control valve housing 85 there thus prevailsatmospheric pressure. This atmospheric pressure is propagated through aconnection line 102 into the compartment or chamber 103 of the reactionunit 87, and furthermore, through the agency of the connection line 104such atmospheric pressure also prevails at the upper compartment 105 ofthe relay valve 58. Relay valve 58 is a conventional type valve of knownconstruction and apart from the housing 106 possesses, as usual, apiston diaphragm or membrane 107, movable closure elements 108, 109 anda closing spring 110. This relay valve 58 is provided because thecontrol valve is not suitable for the throughpassage of large quantitiesof air as such is necessary for the actuation of the piston 111 at thebrake cylinder 57. The work compartment of this brake cylinder 57 isconnected in flow communication via the connection line 112 with thelower compartment 113 of the relay valve 58. The suction or vacuum airinlet 114 is connected by means of the connection line 115 with thevacuum or negative pressure container 97. When the piston diaphragm 107is impinged with atmospheric pressure from the compartment 105 then theclosure elements 108, 109 of the relay valve 58 assume the illustratedposition. Consequently, the chamber 113 communicates with atmosphere,the brake cylinder 57 is vented and therefore the brakes of the trailerare not braked in this condition.

There will now be described the operational condition which prevailswhen the brake light switch 52 is closed by slightly tapping the brakepeddle, but no braking of the tractor, in other words no decelerationthereof, has yet occurred.

Owing to closing of the brake light switch 52, on the one hand thecomplete battery voltage is applied to the brake or stop light 51 sothat such illuminates, and, on the other hand a voltage is applied viathe resistor 63 to the light source 60 so that this light source 60illuminates and the photoresistor 61 is completely impinged with light.Consequently, the resistance of the photoresistor 60 drops to a minimumvalue. This results in the voltage which is positive with respect toground and which appears at the non-inverting input 3 of the operationalamplifier 64 dropping relatively intensely in accordance with thereduction of the resistance of the photoresistor 61. However, such doesnot have any influence upon the current which flows through theimmersion coil 83 since the transistor 65 is alreadycompletely-conductive. In order to prevent dropping of the positivevoltage at the input 3 of the operational amplifier 64, rather toincrease such voltage by an amount so that'the current flowing throughthe immersion coil 83 drops by approximately one-quarter, the junction66 of the input voltage divider is likewise connected through theintermediary of the resistor 74 with the positive pole or terminal ofthe battery 53.

Since the current flow through the immersion coil 83 has dropped byabout one-quarter with the magnetic field of the permanent magnet 82remaining unchanged the axial force transmitted by the immersion coil 83likewise drops by a corresponding amount. Now the tilting moment exertedby the spring 91 upon the rod 83 exceeds the tilting moment exerted bythe immersion coil 83. Accordingly the valve element 86 is now tilted inthe counterclockwise direction, so that this valve element 86 initiallycloses the mouth 99 of the channel 100 and then opens the mouth 95 ofthe suction line 96. Consequently, there is a drop in pressure in thechamber 101 of the control valve 84, the chamber 103 of the reactionunit 87 and the upper chamber 105 of the relay valve 58. A forceequilibrium condition prevails at the reaction piston 88 in the reactionunit 87, which approximately is then the case when the pressure in thecompartment 101 has dropped by about one-quarter of the atmosphericpressure. The same pressure reduction exists at the compartment 105 ofthe relay valve 58. At the relay valve 58 initially the closure element1.09 comes to bear at the seat of the housing 106 and thereafter theclosure element 108 is raised from the closure element 109, resulting inthe fact that the chamber 113 together with the connection line 112 andthe working compartment of the brake cylinder 57 are placed intocommunication with the suction line 96. The equilibrium condition at therelay valve 58 prevails as soon as the pressure equilibrium exists inthe compartment 105 and 113. Thus, at the brake cylinder 57 there comesinto play the negative pressure which amounts to about one-fourth ofatmospheric pressure and the brakes of the trailer vehicle are lightlyapplied.

There will now be described the operations which occur when the tractoris braked owing to actuation of the brake peddle, in other words when adeceleration occurs at the tractor.

Owing to the braking action the circular pendulum 59, the axis ofrotation of which is arranged transverse with respect to the directionof travel, is deflected as a function of the magnitude of the braking ordeceleration and thereby, again as a function of the magnitude of thedeceleration, covers the photoresistor 61 so that the resistance valuethereof increases in proportion to the magnitude of the braking ordeceleration action. With the increase of the resistance value of thephotoresistor 61 the voltage at the junction 66 increases and thereforealso at the input 3 of the operational amplifier 64. Since thetransistor of the power stage is controlled by means of this voltagedrop the current flowing through the immersion coil 83 drops in directrelationship to the amount which the circular pendulum 59 covers thephotoresistor 61. During maximum deceleration the current flowingthrough the immersion coil 83 practically amounts to zero so that, aswill be hereinafter explained, the maximum braking action is initiated.Therefore, in analogy to the known compressed airand vacuum brakes thereis ensured for a braking of the unintentionally released trailer.

At the immersion coil 83 of the transducer 81 which is supplied by theamplifier 65 the current flow is inversely proportional to thedeceleration or braking of the tractor. During increasing decelerationor braking the magnetic force acting upon the immersion coil 83 dropsand in cooperation with the reaction unit 87 there appears at thecompartment 101 of the control valve 84 a correspondingly large negativepressure, similar to what has already been described for the operationalcondition, at which the foot brake is only slightly tapped untilillumination of the brake lights. Just as was the case with thedescription of that mode of operation here also this increased negativepressure is transmitted via the relay valve 58 to the workingcompartment of the brake cylinder 57 where thus the piston 111 isdisplaced by an increased force and thereby exerts a correspondinglygreater braking action upon the wheels of the trailer.

Owing to the special construction of the control valve 84, namely thetiltable mounting of the rod 93 very near to the plane of the closingsurface of the effective valve component 86, this control valve 84 iscapable, even in the presence of only very small control forces, ofcontrolling a pressure stably and free of hysteresis. Furthermore, theconstruction of the control valve provides the additional advantage, incontrast to impact plate systems, that it is relatively free of airlosses once a reference value has been regulated.

With reference now to FIG. 6 there will be described an embodiment ofthe invention wherein at the trailer vehicle there is provided anelectro-magnetically actuated trailer brake 116 of known construction.Here also the brake or stop lights are indicated by reference character51, the brake light switch by reference character 52 and the supplybattery by reference character 53. Further, a braking or decelerationindicator is collectively represented by reference character 117, thisdeceleration indicator 117 incorporating a circular pendulum 118 whichis arranged at the tractor in such a manner that with increasingdeceleration or braking of the tractor an increasing quantity of lightarrives from an electric light source 119 at a photoresistor 120. Inorder to stabilize the supply voltage of the light source 119 there ishere also provided a Zener diode 123 which cooperates with a resistor121. An amplifier arrangement 122 embodies in its circuit an inputvoltage divider consisting of the resistors 124 and 125, the sameoperational amplifier 64 as used and discussed above in conjunction withthe embodiment of FIG. 5, a power stage possessing the two transistors126 and 127, and a feedback voltage divider consisting of the resistors128 and 129. The emitter of the transistor 127 is connected via awinding or coil 130 of the electrically actuated brake device 116 withground. This brake device 116 is ineffectual during such time as nocurrent flows through its winding 130.

The amplifier 122 and the deceleration indicator or transmitter 117 aresupplied via a common supply line or conductor 131 which is connectedwith the brake lights 51 at the brake light switch 52. When the brakepeddle is not actuated the brake light switch 52 is open, the brakelights 51 do not light up and the amplifier 122 as well as thedeceleration indicator 117 do not have any voltage applied thereto.Therefore the winding 130 of the brake 116 also does not carry anycurrent.

Now if the brake peddle is actuated and the stop or brake light switch52 is closed, the stop or brake lights 51 illuminate and the amplifier122 and the deceleration indicator 117 have applied thereto the batteryvoltage through the agency of the supply conductor 131. The light source119 illuminates and as long as no deceleration occurs the photoresistoris not illuminated with light because the circular pendulum 118 coversthe light source 119. Photoresistor 120 is connected parallel to theresistor 124 of the input voltage divider 1241, 125. The resistancevalue of the photoresistor 120 during this phase of operation isrelatively high. The resistors 124 and are chosen such that at thejunction point 132 there is supplied such a voltage which is positivewith respect to ground to the input 3 of the operational amplifier 64through the agency of the protective resistor 75 that at the loadresistor 77 at the output 7 of the operational amplifier 64 a smallvoltage drop occurs which is not capable of controlling the power stagesuch that an appreciable current will flow through the winding or coil130.

As the braking or deceleration action increases the photoresistor 120 ismore intensely impinged with light. inversely with respect to theincrease of the illumination of the photoresistor 120 with light theresistance value of the photoresistor 120 becomes smaller and thevoltage at the junction 132 which is positive with respect to groundincreases in proportion to the deceleration. The voltage drop at theload resistor 77 increases and therefore also the current delivered tothe winding of the brake 116, this current increase being in directrelationship to the deceleration or braking action. This causes theeffective action of the brakes of the trailer to be increased.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and practicedwithin the scope of the following claims, Accordingly,

What is claimed is:

1. A trailer brake control system for a tractor-trailer arrangement,comprising in combination a circular pendulum deceleration transmittermeans installed at the tractor and which, during braking of the tractor,controls the quantity of light received by a photoelement from a lightsource supplied by a constant voltage, so that at said photoelement theresistance thereof increases or decreases in proportion to the momentarydeceleration of the tractor; electronic means in circuit with saiddeceleration transmitter for delivering as a function of the momentaryresistance of said photoelement an electrical signal having an intensitywhich is proportional to the momentary deceleration of the tractor;transducer means which, as a function of such electrical signal, actsupon a braking unit, actuated in proportion to the intensity of suchelectrical signal, and wherein said braking unit incorporates a brakecylinder containing a piston, said transducer means defining anelectro-pneumatic transducer means comprising an electro-dynamictransducer, means for finely mechanically coupling said electro-dynamictransducer substantially reactive free with a control valve, saidcontrol valve cooperating with a reaction unit, and wherein said controlvalve acts through the agency of relay valve means upon said pistonwithin said brake cylinder.

1. A trailer brake control system for a tractor-trailer arrangement,comprising in combination a circular pendulum deceleration transmittermeans installed at the tractor and which, during braking of the tractor,controls the quantity of light received by a photoelement from a lightsource supplied by a constant voltage, so that at said photoelement theresistance thereof increases or decreases in proportion to the momentarydeceleration of the tractor; electronic means in circuit with saiddeceleration transmitter for delivering as a function of the momentaryresistance of said photoelement an electrical signal having an intensitywhich is proportional to the momentary deceleration of the tractor;transducer means which, as a function of such electrical signal, actsupon a braking unit, actuated in proportion to the intensity of suchelectrical signal, and wherein said braking unit incorporates a brakecylinder containing a piston, said transducer means defining anelectro-pneumatic transducer means comprising an electro-dynamictransducer, means for finely mechanically coupling said electrodynamictransducer substantially reactive free with a control valve, saidcontrol valve cooperating with a reaction unit, and wherein said controlvalve acts through the agency of relay valve means upon said pistonwithin said brake cylinder.